tube rectifiers, HexFreds, and the Big Deal

[J. Larry Hendry]

Bill,	This is very interesting reading.  Thanks for sheding some light on
the "It's more than that tube distortion coloration thing."  You are
absolutely correct that one of the most pesky sources of noise induced back
to the power line is any device (usually digital) which has a power supply
which does not utilize the entire sine wave for it's current draw cycle. 
The best analog analogy I can relate to of course is the famous noise
generating incandescent light dimmer.

I was having trouble following the logic that a linear power supply using
solid state diodes would cause distortion of this type.  Then the obvious
hit me like a brick --  the diode does not start conducting until the
voltage magnitude of the sine wave overcomes the voltage required to cause
the diode to connect.  So, at each zero crossing, you have a shut off
period on both sides where neither diode is connecting.  Obviously, this is
not as severe and DC motor varible speed controls and light dimmers, but
still I guess a source of noise nevertheless.

----------
> From: Bill Layer <blayer at uswest.net>
> The sound of tube rectifiers goes to a much deeper level than Zout of the
> power supply. The issues at hand are those of AC power factor, and diode
> switching artifacts. Power factor is a way of quantifying of distortion
of
> the 50 or 60 Hz wavform on the AC powerline. Distortion can be caused by
> sevral sources, the most common being inductive or electronic loads.
> Electronic loads, especially solid state, cause heavy peak currents, with
> abrupt switching. Not only does this distort the powerline waveform, but
> the diodes themselves radiate noise and RF energy which also effects the
> sound. 
> 
> In any event, as distortion of the powerline waveform increases, the out
of
> phase harmonics begin to cancel (attenuate) the current of the
fundamental,
> and thus the line loses it's abilty to deliver full power. Under the
right
> conditions, it might be possible to measure nominal line voltages, yet
not
> be able to draw productive power. There is an excellent article on this
> subject by Marty DeWulff in "Bound for Sound". 

OK, tell us more about how these diodes accomplish their task so quietly.

> Now in contrast to the harsh, abrupt nature of solid-state rectifiers,
tube
> diodes are soft, gentle and quiet. They generate little or no noise or
RF,
> and are equally kind the the powerline waveform. There IS a solid state
> near-equivalent to the tube rectifer, it is called a HexFred diode. I use
> these in all of my audio amps, and the difference is HUGE. If you don't
> believe me, call up digi-key and order a few; they're only a buck or two
> each. Use them to replace the 1N4004s in your whatever, and then tell
> everyone what you think.
> 
> The implications of this are of course, massive. Using tube rect's or
> HexFreds not only improves the sound of the particular piece, but helps
out
> the entire system by preserving the integrity of the power waveform, and
> reducing noise pollution. Computers are a serious offender here; it's no
> wonder that at Atma-Sphere and Mapleshade studios, all digital
electronics
> are shut down during recording or mastering sessions. If you own
computers,
> try that one yourself...

Yes, not only computers, but don't forget about the the laser printer !!
 
> Finally, if you're still not convinced, try this one. Warm up you stereo
> (the cheaper, the better...) and listen to a short piece that you've
heard
> many times. Pay special attention to anything that strikes you: parts
which
> are bright or annoying, parts which come through well, with feeling.
Places
> where the bass seems the most liquid.
> 
> Now, pull the plugs and give the prongs a quick wipe with light oil -
like
> LPS or even WD-40. The thinner the coat the better. Plug-in and go around
> again with the same piece; if you aren't sure what you just heard,
clean-up
> and do the test again (might be tricky in same outlet...). I'll be
> interested to hear your reactions, and theories on what happened.

Now, you are going to have to give me more of an explanation before I start
down that road.  All my stuff is plugged in to the back of racks coming
from a dedicated circuit from the box.

By the way, since we are on this subject, I would like to point out that
keeping all studio loads on a common neutral and common ground star
connected from your box is a good way to avoid some of the most basic
ground loop problems.  Another great advantage of the dedicated circuit is
the absolutely best lightning protection that you can install for only $30.
 For about $30 you can buy a 30 amp three pole safety disconnect (similar
to the 2 poles used for air conditioner safety switches).  My studio
circuit goes through this switch which stays turned off at all times I am
not using the equipment.  Although it is not a replacement for power line
conditioning or surge protection, it is 100% the most effective lightning
protection you can install (unless you continue to use the equipment during
a storm)... :)

Now, back to the subject.  Bill you have only wet my appetite.  More
please. 
Larry Hendry